1. Field of the Invention
The present invention relates to an MRAM (Magnetic Random Access Memory) having a magnetoresistive element.
2. Description of the Related Art
In recent years, an MRAM (Magnetic Random Access Memory) using a TMR (Tunnel Magneto-Resistance) effect has been proposed as a kind of semiconductor memory.
In each memory cell of an MRAM, an MTJ (Magnetic Tunneling Junction) element serving as an information storage element is formed at the interconnection between a bit line and a word line. In a data write mode, a current is supplied to each of a selected bit line and a selected word line. Data is written in the MTJ element of the selected cell located at the intersection between the selected bit line and the selected word line by a composed magnetic filed generated by the currents. In a data read mode, a read current is supplied to the MTJ element of a selected cell so that “1” or “0” data is read out in accordance with a resistance change in the magnetized state of the MTJ element.
In a data write in such an MRAM, the write current field may influence even a semi-selected cell which is selected in correspondence with only one of the selected bit line and selected word line. This may cause a write error in the semi-selected cell so that a problem of disturbance may be posed. Avoiding the problem of disturbance is regarded as one of most significant challenges in developing an MRAM.
As a solution to the problem of disturbance, a toggle MRAM using two recording layers anti-ferromagnetically coupled with each other has been proposed (e.g., U.S. Pat. No. 6,545,906). In this toggle MRAM, however, the write current value is large impractically. As described above, in the conventional MRAM, it is difficult to reduce the write current while suppressing any write error.